Ball mill for continuous sifting and grinding



. 2, 1949. r G. J. MITCHELL 24 BALL MILL FOR CONTINUOUS SIFTING AND GRINDING Filed Aug. 19, 1944 3 Sheets-Sheet 2 1949- G. J. MITCHELL BALL MILL FOR CONTINUOUS SIFTING AND GRINDING Filed Aug. 19, 1944 3 Sheets-Sheet 3 M iv m Q w m w 1 iv m B 0% iv m Q Q 0 0 0 l! 00 0 a .lllhnv 0 w 00 0 Q WA. Z lu 0 Q a 0 .iV 0 2 4 0 Q 0 4 5 a I. I M .6 .0 w 5 0 M 5 /WV J E 0 w 0 F.

Patented Aug. 23, 1949 BALL MILL FOR CONTINUOUS SIFTING AND GRINDING George J. Mitchell, Minneapolis, Minn., asslgnor to General Mills, Inc., a corporation of Delaware Application August 19.1944, Serial No. 550,288

2 Claims. (Cl. 241-80) This invention relates to ball mills and particularly to those where the material to be ground is continuously circulated.

An object of this invention is to provide a ball mill in which the material to be ground is circulated through the mill, is sifted, and the overs are continuously fed back to the entering end of the mill for further grinding, thereby continuousl effecting removal of the finely ground material from the coarser which speeds up the grinding operation.

This and other objects, as will hereinafter appear, are accomplished by this invention which is fully described in the following specification and shown in the accompanyin drawings in which:

Figure l is a longitudinal vertical section through a machine embodying the invention;

Figs. 2 and 3 are vertical transverse sections on the lines 2-2 and 3--3 respectively on Fig. 1;

Fig. 4 shows a fragmentary end elevation of the receiving end of the machine; and

Fig. 5 is a fragmentary View similar to that of Fig. 4 showing certain details thereof.

The embodiment illustrated comprises a framework Ill, I2 of wood or the like having legs I4, I6

for supporting the machine on the floor. A shaft I8 is suitably journaled in bearings 20, 22 which are carried by the main frame, this shaft being driven by means of a sprocket 24 and chain 26 from a sprocket 28 and through a suitable gear reduction 39 operated by a motor 32.

Spiders 40. 42 are keyed on the shaft I8 and their peripheries 44 and 46 respectively are preferably circular in shape. These spiders also carry through-bolts 48 on which are secured clips 50 about wh ch are secured bands 52 of the same general configurat on as the peripheries 44, 46. A su table screen 54 of any well known type is thcn secured about the peripheries 44, 46 and the bands 52.

The ends of the machine are c osed by means of \"a-.ls C0, 62 and plates 64, .66. The wall 60 carries an angular strip which lies inside a shoulder 12 within the peripher 44. A feed chute I5 feeds material to be ground through the spider 40 and into the space enclosed by the screen 54.

The ball mill itself will now be described. It consists essentially of a metal drum 80 having flights 80a therein, and carried by spiders B2, 84 on the shaft I8 and closed at the entering end of the machine by a head 86 which is provided with perforations 8B for the purpose which will later be pointed out.

At the opposite end the drum has a frustoinsertion of a chute 94 which has a sleeve 96 freely journaled on the shaft I8 between suitable collars 98 and which is provided with a weight I00 for holding the chute in the vertical position shown in Fig. 1. v

Scoops I02, secured on the through-bolts 48 are inserted to pick up material at the righthand end of the screen as shown in Fig. 1 and to carry it up and drop it on the chute 94 where it then passes into the right-hand end of the drum.

Referring now particularly to Figs. 2 and 3, the I provide a housing for a. screw conveyor I I8 which is driven from the shaft I8 by means of sprockets I22 and I24 and with chain I26.

The operation of the machine is as follows. A quantity of steel balls or the like I30 are placed in the drum which is then caused to rotate by means of the motor 32. Materials to be ground such as bran is fed into the chute 16. As the screen rotates, this material will then travel to the right and any fine material therein passes through the screen 54. The overs of the screen are then picked up by the scoop I02 and dumped on thechute 94 where they pass to the righthand end of the drum. As the drum is rotated this material then passes to the left through the drum and 'is continuously ground by the action of the balls as it passes to the left and outthrough the openings 88 which are large enough to permit the material'being ground to pass through but which retain the balls. This same material again passes over the screen where the finer portions are removed and the coarser are through the ball mill until they are ground sufconical end 90 which is open at 92 to permit the ficiently to pass through the screen. The mate rial passing through the screen is propelled by the conveyor II8 to a chute I32 beneath whlch'a bag or the like I34 may be secured for catching the raw material. v

A well known cleaning brush I35 is employed to sweep the reels and is mounted upon a shaft I36 journaled in bearing I31 which are in the form 01 arms pivoted 3 at I" and adjustable by means of a screw I39. The shaft I36 extends through an arcuate slot I which is concentric -to the pivot I38. This mechanism permits the adjustment of said .brush Ill relative to it" screen 6|.

The brush I is driven through the well known gear train as follows: a gear I4I secured on the shaft I8 of. the machine drives a pinion Illa mounted upon a sleeve I42 journaled on a stub shaft I43, and the numeral I indicates a pulley that is also journaled upon a sleeve I42 and drives a pulley I45 that is keyed to the shaft I36 through a belt I46- Said belt I46 is provided with a customary belt tightener I".

It will, be noted. that the machine housing is provided with a vent pipe I 48 for the purpose of removing dust from the machine. In reference to the walls of the machine I I0 and II 2 it will be noted that these walls are removable sections also lowered as illustrated-for the purpose oi" venting the machine.

While I have'shown and described but a single embodiment of my invention. it is to be understood that it is capable of many modifications. Changes, therefore, may be made which do not depart from the spirit and scope of my invention as disclosed in the appended claims.

Iclaim as my invention:

1. A ball mill comprising a tubular drum mounted for rotation about a substantially horizontal axis, balls therein, a tubular screen mounted for rotation outside the drum, one end of the drum being perforated to permit the passage of material being ground to the head end of the screen while the balls are retained, means for transferring material from the tail end of the screento the head end of the drum, and means for feeding material to be ground to the head end of the screen so that it passes through the screen before grinding.

. .2. A ball mill comprising a shaft, a tubular drum mounted thereon for rotation about a substantially horizontal axis, balls withinthe drum, a tubular screen mounted for rotation outside the drum, one end of the drum being perforated to permit the passage of material being ground to the head end of the screen while theballs are retained, a chute freely journaled onthe shaft and having a weight maintaining the chute in an upright position regardless of rotation of the shaft, said chute extending upwardly and outwardly from a point inside the entering end of the drum to a point in the discharge end of the screen, and scoops mounted within the screen and adapted to lift said material and deposit it on the chute sothat it flows into the entering end of the drum.

- GEORGEJ. MITCHELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

